1. Field of the Invention
The present invention relates to a GMR read sensor with an antiparallel (AP) coupled free layer structure and antiparallel (AP) tab ends for a narrow track read head.
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which includes a rotating magnetic disk, a slider that has a magnetic head assembly which includes write and read heads, a suspension arm above the rotating disk and an actuator arm. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the actuator arm swings the suspension arm to place the write and read heads over selected circular tracks on the rotating disk where signal fields are written and read by the write and read heads. The write and read heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
An exemplary high performance read head employs a giant magnetoresistance (GMR) read sensor for sensing magnetic signal fields from the rotating magnetic disk. The GMR read sensor comprises a nonmagnetic electrically conductive spacer layer that is sandwiched between a ferromagnetic pinned layer and a ferromagnetic free or sense layer. An antiferromagnetic pinning layer typically interfaces the pinned layer for pinning the magnetization of the pinned layer 90° to an air bearing surface (ABS) of the read sensor wherein the ABS of the read sensor is an exposed surface of the read sensor that faces the rotating disk. First and second hard bias and lead layers are typically connected to the read sensor for conducting a sense current therethrough. The magnetization of the free layer is free to rotate upwardly and downwardly with respect to the ABS from a quiescent or zero bias point position in response to positive and negative signal fields respectively from the rotating magnetic disk. The quiescent position of the magnetization of the free layer, which is parallel to the ABS, is when the sense current is conducted through the read sensor without signal fields from the rotating magnetic disk.
When a sense current is conducted through the read sensor, electrical resistance changes of the sensor cause potential changes that are detected and processed as playback signals by processing circuitry. The sensitivity of the read sensor is quantified by a giant magnetoresistance (GMR) coefficient ΔR/R where ΔR is the change in resistance of the read sensor from minimum resistance (when magnetizations of free and pinned layers are parallel to each other) to maximum resistance (when magnetizations of the free and pinned layers are antiparallel to each other) and R is the resistance of the read sensor at minimum resistance.
First and second hard bias and lead layers are typically connected to first and second side surfaces of the read sensor, which connection is known in the art as a contiguous junction. This junction is described in commonly assigned U.S. Pat. No. 5,018,037. The first and second hard bias layers longitudinally stabilize the magnetization of the free layer of the GMR sensor in a single domain state which is important for proper operation of the GMR sensor.
Unfortunately, as the track width of the GMR sensor decreases the response of the magnetization of the free layer of the GMR sensor also decreases. This is due to the effect of the first and second hard bias layers on the GMR sensor. When the track width of the GMR sensor is sufficiently wide, such as 1.0 μm, only first and second side portions of the GMR sensor are stiffened by the first and second hard bias layers because the magnetization of the first and second hard bias layers decay into the first and second shield layers. However, when the track width of the GMR sensor is very narrow, such as 0.1 μm, the GMR sensor is stiffened in its operation from side to side so that it is less responsive to signal fields from the moving magnetic medium. There is a strong-felt need for longitudinally stabilizing the GMR sensor with first and second hard bias layers without stiffening the operation of the GMR sensor to signal fields.